Hi,
A couple questions pertaining to bio-type 3/4d sequences:
1) In the HNCO/HNCA type experiments, 13C decoupling during 13C
evolution falls along either off-resonance Seduce cpd during evolution
or a single off-resonance 180 pulse (with appropriate off-resonance
compensation) centered in the evolution period.
While I can rationalize theoretical differences between the development
of 2-spin 13C'-13Ca coherence and associated relaxation behavior, are
there any significant _practical_ differences between these decoupling
methods, especially as regards to 13C lineshape, ease of setup,
ramifications of mis-setup, or power loading on the C/N coil of a
cryoprobe?
2) More Bruker-specific, are there differences between using spoffs to
shift a pulse, using a pre-generated shifted pulse, and moving the
transmitter via frequency lists? I had thought that (on older
spectrometers, at least), moving the transmitter could cause loss of
phase coherence, whereas shifting pulses would not. I imagine that some
of the differences are also historical. Given reasonably new hardware
(DRX and up), and software (Xwin 3.5), what are the differences between
these methods? I'm assuming that spoffs generates phase-modulated
pulses. For amplitude-modulated pulses, using pre-generated waveforms
seems easiest. For other cases (e.g. HNCO), is there a practical
difference?
Thanks for any comments.
David Horita
-----------------------------
David A. Horita, Ph.D.
Department of Biochemistry
Wake Forest University School of Medicine
Winston-Salem, NC 27157-1016
Tel: 336 713-4194
Fax: 336 716-7671
email: dhorita@wfubmc.edu
web: http://www1.wfubmc.edu/biochem/faculty/Horita.htm/
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